1. Field of the Invention
This invention relates to fuel injection for an engine, and more particularly to a fuel injection system that is suitable for an outboard motor.
2. Description of Related Art
In the interest of improving engine performance and particularly fuel efficiency and exhaust emission control, many types of engines now employ a fuel injection system for supplying fuel to the engine. In this system, generally fuel is injected into an air induction device by a fuel injector. This fuel injection has the advantages of permitting the amount of fuel delivered for each cycle of the engine to be adjusted. In addition, by utilizing the fuel injection system, it is possible to maintain the desired fuel air ratio under a wide variety of engine running condition.
The amount of fuel injected by the fuel injector is usually controlled by a control device in response to the engine running conditions. More specifically, the fuel is delivered to the fuel injector by a fuel pump under a certain fixed pressure and duration for injection per unit time, i.e., a duty ratio, is controlled by the control device so that any required amount can be measured. Strict control of the fuel amount is quite important for stable operation of the engine.
Some outboard motors incorporate such a fuel injection system. Typically outboard motors are constructed to be easily unmounted from the associated watercraft for being carried to, for example, a repair factory. Engines for the outboard motors, thus, should be as compact as possible despite that they are required to be quite powerful relative to such compact bodies. Because of this reason, the engines for the outboard motors are not allowed to employ a large-scale cooling system. In addition, since the engines are generally enclosed in protective cowlings, the heat radiated from the engines during operations is likely to be retained within the cowlings. Under the circumstances, bubbles or vapor can appear in the fuel that will be injected by the fuel injector and may harm the strict control of the fuel amount.
In order to inhibit the vapor from entering the fuel, usually a vapor separator is provided in the fuel injection system that is employed for the engine of the outboard motor. The fuel injection system includes, therefore, a main fuel supply tank disposed in the hull of the associated watercraft, and the vapor separator mounted on, for example, the engine. The fuel in the main tank is delivered to the vapor separator with a low pressure fuel pump and then the vapor, if any, is separated from the fuel. The fuel is delivered to the fuel injector with a high pressure pump and injected into the air induction device by the fuel injector. The excess fuel that has not been injected returns to the vapor separator through a return passage.
The high pressure fuel pump is usually unified with an electric motor, which drives the pump, as a pump unit. The pump unit is usually positioned within the vapor separator because the engine can hardly provide a space for disposing the fuel pump out of the vapor separator. The electric motor, however, is likely to produce heat therein when operating. The heat, therefore, may be conducted to the fuel. Due to this arrangement and construction, the problem that the vapor can be made in the fuel may still not be completely resolved.
In addition, the high pressure pump is operated to deliver the maximum amount of the fuel that meets the highest engine speed and/or the largest load. Thus, the lower the engine speed and/or the smaller the load, the greater the excess fuel will return to the vapor separator. This situation leads to the increase of heat in the fuel more and more.
As one way to resolve the problem, a resistor is provided in a control circuit or controller that drives the electric motor, and the resistor can be switched over when the engine is operated under a low engine speed and/or low load to reduce current in the circuit. Alternatively, a variable resistor also can be employed for reducing the current under the same condition. This may be advantageous for decreasing the heat in the fuel. However, on the other hand, this approach increases the manufacturing cost of the engine and eventually the total cost of the outboard motor.
A similar problem may occur with other engines, irrespective of being incorporated with outboard motors, inasmuch as the pump unit is disposed in the vapor separator. The problem may also occur if the heat produced by the pump unit is conducted to the fuel by some means even though the unit is not placed within the vapor separator.
A need therefore exists for an improved fuel injection control that reduces undesirably heating of the fuel within the fuel supply system without increasing the cost therefor.
In accordance with one aspect of the present invention, an internal combustion engine comprises a cylinder body defining a cylinder bore in which a piston reciprocates. A cylinder head is affixed to an end of the cylinder and defines a combustion chamber with the cylinder head and the piston. A fuel injector supplies fuel to the combustion chamber. A fuel pump delivers the fuel from a reservoir to the fuel injector. An intermittently powered electric motor drives the fuel pump.
In accordance with another aspect of the present invention, a fuel injection system is provided for an internal combustion engine having a combustion chamber. The system comprises a fuel injector supplying fuel to the combustion chamber. A fuel reservoir is arranged to store the fuel therein. Means are provided for delivering the fuel in the reservoir to the fuel injector. The delivering means operates intermittently.
In accordance with a further aspect of the present invention, a fuel injection system is provided for an internal combustion engine having a combustion chamber. The system comprises a fuel injector supplying fuel to the combustion chamber. A fuel reservoir is arranged to store the fuel therein. A fuel delivery mechanism delivers the fuel in the reservoir to the fuel injector. A control device activates the delivery mechanism intermittently.
In accordance with still a further aspect, a method of operating an internal combustion engine is provided. The engine has a combustion chamber, a fuel injector, and a fuel supply mechanism for supplying the fuel to the fuel injector. The fuel supply mechanism is activated intermittently in response to the amount of the fuel needed. The method involves sensing at least one of the engine speed and the engine load, and determining the amount of fuel to be injected by the fuel injector toward the combustion chamber.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment which follows.